Add option to check if column is null by name

[4brunu]

While using the library I wanted to check is a column is null, but only found a method that allow to check it by index, so I added one that is similar but check by the column name.

I have also added the tests to it.

[coveralls]

Coverage increased (+0.06%) to 97.43% when pulling f022c6a on 4brunu:master into 401b736 on SRombauts:master.

[SRombauts]

Thanks @4brunu!

I merged it as-is, but I will rework some of it:

• removing const on isColumnNull() does not seems right
• I believe duplicating code to map indexes to names is not a good idea either

Cheers!

[4brunu]

Hi @SRombauts, sure, no problem at all :)

Just to elaborate on some of the decisions:

• I removed const because it was giving a compiler error. I didn't understand why, could you elaborate on that please?
• I tried to do that, but I ended up reverting that because it was resulting in some issues, due to my lack of c++ experience.

Thanks for the amazing library 👍

[SRombauts]

The const compiler error was weird: the problem is that we know have two overloaded functions isColumnNull(), one taking an (int), the second one taking a pointer (const char*).
Thus when calling it with zero isColumnNull(0) the compiler has to decide witch one is the best one since 0 is also a nullptr.

There is no problem if the two methods are both const or not const, but there is an error if only one is const: I think that the compiler is not able to decide witch one is the best are they are not real overload...

[4brunu]

Thanks a lot for the explanation :)